BACK in 2009, as excavators cut though the chalk at Ridgeway Hill in preparation for the Weymouth relief road, they made a shocking discovery.

In a shallow grave was a tangled mass of decapitated skeletons, their heads piled to one side.

So important was this grisly discovery that it has just featured in the National Geographic documentary Viking Apocalypse, in which a team of archaeological experts scrutinise every skeleton to find more answers about these people and when, how and why they died.

Burial archaeologist Angela Boyle said: “It’s a unique find. There’s nothing to parallel this, and that makes it very exciting. It’s also quite sad and quite moving and emotional as clearly these individuals met a very unhappy end.”

Weapons historian Mike Loades said it was “an atrocity – a terrible moment in history. Something really bad happened here”.

The mass grave of 54 skeletons and 51 skulls was discovered where the Ridgeway and a Roman road cross but such was the age of the bones, this ancient murder mystery was more a matter for archaeologists than police.

Carbon dating revealed the victims almost certainly died between 980 – 1030AD – one of the most turbulent times in British history.

A thousand years ago, Anglo Saxon England was under attack by Vikings from Scandinavia, looking for riches on our shores.

Dr Britt Baillie, from the University of Cambridge, said: “The whole Viking period started here in Dorset, as the first recorded Viking raid on England took place on Portland with three ships landing here in 789.”

Wave after wave followed, and eventually 100 years of conflict was ended when a peace treaty was signed and the Vikings established their own kingdom of Danelaw in the north, with Anglo Saxon England to the south and west.

All the skeletons found on the Ridgeway were male so it was most likely they were a band of warriors.

And as Vikings returned to Dorset again and again, it was initially thought the bones were those of Anglo Saxons defending themselves from the Scandinavian sea pirates.

Yet isotope data from their teeth revealed that the victims spent their childhood in a cold climate. They were Scandinavian and therefore the bodies were those of Vikings.

This information challenged our beliefs that Anglo Saxons were peaceful farmers. Further data from the bones indicated their upper bodies were particularly well-developed, and consistent with the shape of a rower – so they were possibly the crew from a Viking ship.

Some of the victims had filed teeth, modelling themselves on King Harald Bluetooth (who filed his teeth and filled the ridges with blue paste for effect) and the Jomsvikings – a band of mercenaries who would fight for any lord able to pay their substantial fees.

Dr Baillie said the murders could have taken place during the reign of Aethelred the Unready.

Following a series of attacks he ordered all Danish men in England to be killed on November 13 – St Brice’s Day – in 1002, which became the St Brice’s Day massacre.

No artefacts were found with the corpses implying they were stripped naked when they were thrown into the pit.

They had no battle scars except well-defined cut marks to the right temporal which were the result of their beheading.

Their hands hadn’t been tied together so experts wondered if they had been decapitated post mortem, yet further forensics revealed they had been beheaded from the front to the back and it happened when they were alive.

The most likely execution implement was a sword with edges of forged, hardened steel which was the sort of weapon that would have been handed down through generations.

This method of slaughter at least afforded them a ‘respectful’ death, said experts. Jomsviking warriors in this period wanted to be brave enough to look their executors in the eye as they died.

Another question raised was just why this exposed hilltop location was used as an execution site. Landscape archaeologist Alex Langlands explained: “It’s situated on an important crossroads of the ancient Ridgeway and a Roman road – probably the most important in the county. The Ridgeway came into being in the prehistoric period, but of course by the time we get to our period it’s forming a major highway.

“All along the Ridgeway are ancient burial mounds, known as barrows. To kill men on or near a barrow would have given it a darker and more sinister association.”

Alex believes another reason is that the execution site is a highly visible place with routes to Portland, Weymouth and Dorchester with plenty of passing ‘traffic’.

The fact that three skulls were missing among the bones suggest that they were placed on stakes as a warning to others.

Ultimately the massacre was in vain as the Vikings eventually took over the whole of England, but for researchers such as Dr Britt Baillie, it was a welcome find.

"A piece of English history has been forgotten for a thousand years and now we can piece it together,” she said.